This invention relates to a facsimile communication system for transmitting images of pictures and writings at high speed.
A picture signal originating from any of the picture elements generally has a correlation with picture elements located in the two-dimensional area close to that picture element. The term picture element used herein and in the appended claims refers to the elementary area of any picture and that of any writing. By knowing the peripheral pattern formed by those adjacent picture elements (which are called hereinafter "reference picture elements"), it is possible to decrease the information content which is the effect of the two-dimensional prediction.
In conventional facsimile communication systems employing two-dimensional prediction, the transmitting side includes a single prediction converter for calculating a predicted value for an object picture element from the associated binary picture signals in accordance with a predetermined prediction function and the receiving side also includes a single inverse converter corresponding to the prediction converter. On the other hand, it is desirable to change the scanning resolution depending upon the fineness of the subject copy, that is, the picture or writing to be scanned, encoded and transmitted. When the scanning resolution is changed, the object picture element to be predicted may vary in its distance from and/or its relative positions to its reference picture elements. Under these circumstances, if the prediction function remains unchanged, an optimum prediction can not be effected. In other words, the probability of the occurrence of disagreeing predictions increases. This increases the number of encoding operations when encoding is effected each time a predicted value disagrees with the actual value. Thus the degree of compression has been reduced.
Also in the prior art prediction, the four picture elements surrounding each object picture element have been selected to be the reference picture elements for prediction purposes and it has been assumed that any boundary between white and black picture elements is in the form of a straight line parallel to a row or a column of picture elements. However, pictures and writings include many tilted boundaries running between white and black picture elements, and the predictions are inevitably erroneously effected on both sides of such a tilted boundary.
Accordingly, it is a general object of the present invention to eliminate the disadvantages of the prior art practice was described above.
It is an object of the present invention to provide a new and improved fascimile communication system having a high efficiency by effecting the optimum prediction of picture elements constituting the total picture or writing area.
It is another object of the present invention to provide a new and improved facsimile communication system capable of changing scanning resolution in accordance with the fineness of the picture or writing to be transmitted and effecting optimum prediction of picture elements dependent upon the changed scanning resolution thereby effecting prediction of the picture elements suited to the scanning resolution and improving the data compression factor.
It is still another object of the present invention to provide a new and improved facsimile communication system for preventing erroneous prediction of picture elements to increase the prediction efficiency by increasing the resolution with which a picture or a writing is scanned.